Phosphorus (revised)

PHOSPHORUS (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Phosphorus is found in Group 15 (VA) of the periodic table. The periodic table is a chart that that shows how chemical elements are related to each other. Phosphorus is part of the nitrogen family along with nitrogen, arsenic, antimony, and bismuth.

Phosphorus was first discovered in 1669 by German physician Hennig Brand (ca. 1630-92). Brand is somewhat famous in chemistry. He is sometimes called the last of the alchemists. Alchemy was a kind of pre-science that existed from about 500 B.C. to about the end of the 16th century. Alchemists wanted to find a way of changing lead, iron, and other metals into gold. They also wanted to find a way of having eternal life. Alchemy contained too much magic and mysticism to be a real science. But it developed a number of techniques and produced many new materials that were later found to be useful in modern chemistry.

SYMBOL
P

ATOMIC NUMBER
15

ATOMIC MASS
30.97376

FAMILY
Group 15 (VA)
Nitrogen

PRONUNCIATION
FOS-fer-us

Brand was convinced that the key to changing metals into gold could be found in urine. He decided to look for the "magic substance" that could change lead into gold in urine. In the process of heating and purifying urine, he obtained phosphorus.
The discovery was important because it was the first time someone had discovered an element not known to ancient peoples. In that regard, Brand was the first person who could be called the discoverer of an element.

Phosphorus is a fascinating element that occurs in at least three very different forms. If left exposed to the air, it catches fire on its own. It also glows in the dark. Today, its most important use is in the manufacture of phosphoric acid (H3PO4). Phosphoric acid, in turn, is used to manufacture fertilizers and a number of other less important products.

Discovery and naming

Phosphorus and its compounds may have been known before Brand's discovery. Old manuscripts refer to materials that glow in the dark. The word used for such materials today is phosphorescent. Early Christians noted the use of "perpetual lamps" that glowed in the dark. The lamps may have contained phosphorus or one of its compounds.

Still, Brand was the first to record the process of making pure phosphorus. No one knows how he decided that urine might contain a chemical that could be used to turn lead into gold. His experiments to find such a chemical were, of course, a failure. But he made an accidental discovery along the way. That discovery was a material that glowed in the dark: phosphorus.

Scientists were fascinated when they heard of Brand's discovery. They tried to repeat his research. Some tried to talk him into selling his discovery to kings and princes. The new element seemed to be a way of getting rich and becoming famous.

But Brand was never interested in these ideas. Instead, he gave away all of the phosphorus he prepared. Other scientists soon began to experiment with the element. One of the first discoveries they made was how dangerous phosphorus is. One scientist wrote that a servant left some phosphorus on top of his bed one day. Later that night, the bed covers burst into flame. The phosphorus had caught fire by itself!

Eventually, Brand's method of making phosphorus became widely known. The element joined iron, gold, silver, arsenic, and the handful of other elements known to early chemists.

Little is known about what happened to Brand after his discovery. In fact, there is no record of where or when he died.

Physical properties

Phosphorus exists in at least three allotropic forms. Allotropes are forms of an element with different physical and chemical properties. The three main allotropes are named for their colors: white phosphorus (also called yellow phosphorus), red phosphorus, and black phosphorus (also called violet phosphorus). These allotropes all have different physical and chemical properties.

White phosphorus is a waxy, transparent solid. Its melting point is 44.1°C (111°F) and its boiling point is 280°C (536°F). It has a density of 1.88 grams per cubic centimeter. If kept in a vacuum, it sublimes if exposed to light. Sublimation is the process by which a solid changes directly to a gas when heated, without first changing to a liquid. White phosphorus is phosphorescent. It gives off a beautiful greenish-white glow. It does not dissolve well in water, although it does dissolve in other liquids, such as benzene, chloroform, and carbon disulfide. White phosphorus sometimes appears slightly yellowish because of traces of red phosphorus.

Red phosphorus is a red powder. It can be made by heating white phosphorus with a catalyst to 240°C (464°F). A catalyst is a substance used to speed up or slow down a chemical reaction without undergoing any change itself. Without a catalyst, red phosphorus sublimes at 416°C (781°F). Its density is 2.34 grams per cubic centimeter. It does not dissolve in most liquids.

Black phosphorus looks like graphite powder. Graphite is a form of carbon used in "lead" pencils. Black phosphorus can be made by applying extreme pressure to white phosphorus. It has a density of 3.56 to 3.83 grams per cubic centimeter. One of its interesting properties is that it conducts an electric current in spite of being a non-metal.

Brand was convinced that the key to changing metals into gold could be found in urine. Instead, he found phosphorus.

Chemical properties

White phosphorus is the form that occurs most commonly at room temperatures. It is very reactive. It combines with oxygen so easily that it catches fire spontaneously (automatically). As a safety precaution, white phosphorus is stored under water in chemical laboratories.

Phosphorus combines easily with the halogens. The halogens are the elements that make up Group 17 (VIIA) of the periodic table. They include fluorine, chlorine, bromine, iodine, and astatine . For example, the reaction between phosphorus and chlorine is:

Phosphorus also combines with metals to form compounds known as phosphides:

White phosphorus combines with oxygen so easily that it catches fire automatically. As a safety precaution, white phosphorus is stored under water in chemical laboratories.

Occurrence in nature

The abundance of phosphorus in the Earth's crust is estimated to be 0.12 percent, making it the 11th most common element. It usually occurs as a phosphate. A phosphate is a compound that contains phosphorus, oxygen, and at least one more element. An example is calcium phosphate, Ca3(PO4)2.

The only important commercial source of phosphorus is phosphate rock. Phosphate rock is primarily calcium phosphate. The United States is the largest producer of phosphate rock in the world. In 1996, 13,300,000 metric tons of phosphate rock were mined in the United States. That amounted to about a third of the world's total phosphate rock.

Isotopes

Only one naturally occurring isotope of phosphorus exists, phosphorus-31. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

Six radioactive isotopes of phosphorus are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

One radioactive isotope, phosphorus-32, has applications in medicine, industry, and tracer studies. A tracer is a radioactive isotope whose presence in a system can easily be detected. The isotope is injected into the system where it gives off radiation. The radiation is followed by means of detectors placed around the system.

Phosphorus-32 is especially useful in medical studies, because phosphorus occurs in many parts of the body. Radioactive phosphorus can be used as a tracer to study parts of the body as well as chemical changes inside the body. Radioactive phosphorus can also determine how much blood is in a person's body. It can also help locate the presence of tumors in the brain, eyes, breasts, and skin. Finally, it is sometimes used to treat certain
forms of cancer. Radiation given off by the phosphorus-32 may kill cancer cells and help slow or stop the disease.

Phosphorus-32 is important in a variety of scientific studies. For example, it is added to tires when they are made. Then, the radiation it gives off can be studied as the tires are used. This information tells where the tire wears out and how long it takes to wear out.

Extraction

It is possible to make pure phosphorus from phosphate rock. The rock is mixed with sand and coke (pure carbon). The mixture is then heated in an electric furnace. An electric furnace is a device for producing very high temperatures. Pure phosphorus is produced in this reaction. It escapes from the mixture as a vapor (gas). The cooled vapor solidifies into white phosphorus. The reaction is:

Radioactive phosphorus helps locate the presence of tumors in the brain, eyes, breasts, and skin.

This reaction is not very important because pure phosphorus has few uses. The most important compounds of phosphorus are all made from phosphate rock or calcium phosphate. Therefore, the most important step in producing "phosphorus" is
simply to separate pure calcium phosphate from phosphate rock. This can be done fairly easily.

Uses and compounds

In 1996, 91 percent of all the phosphate rock mined in the United States was used to make fertilizer. Modern farmers use enormous amounts of synthetic (artificial) fertilizer on their crops. This synthetic fertilizer contains nitrogen, phosphorus, and potassium, the three elements critical to growing plants. These elements normally occur in the soil, but may not be present
in large enough amounts. Adding them by means of synthetic fertilizer helps plants grow better. Most farmers add some form of synthetic fertilizer to their fields every year. This demand for synthetic fertilizers accounts for the major use of phosphorus compounds.

Phosphorus and its compounds have other uses. These uses account for about 10 percent of all the phosphorus produced. For example, the compounds known as phosphorus pentasulfide (P2S5) and phosphorus sesquisulfide (P4S3) are used to make ordinary wood and paper safety matches. These compounds coat the tip of the match. When the match is scratched on a surface, the phosphorus pentasulfide or phosphorus sesquisulfide bursts into flame. It ignites other chemicals on the head of the match.

Another compound of phosphorus with a number of uses is phosphorus oxychloride (POCl3). This compound is used in the manufacture of gasoline additives, in the production of certain kinds of plastics, as a fire retardant agent, and in the manufacture of transistors for electronic devices.

Health effects

Phosphorus is essential to the health of plants and animals. Many essential chemicals in living cells contain phosphorus. One of the most important of these chemicals is adenosine triphosphate (ATP). ATP provides the energy to cells they need to stay alive and carry out all the tasks they have to perform. Phosphorus is critical to the development of bones and teeth. Nucleic acids also contain phosphorus. Nucleic acids are chemicals that perform many functions in living organisms. For example, they carry the genetic information in a cell. They tell the cell what chemicals it must make. It also acts as the "director" in the formation of those chemicals.

The daily recommended amount of phosphorus for humans is one gram. It is fairly easy to get that much phosphorus every day through meat, milk, beans, and grains.

Two phosphorus compounds are used to coat the tip of a match.

On the other hand, elemental phosphorus is extremely dangerous. Elemental phosphorus is phosphorus as an element, not combined with other elements. Swallowing even a speck of white phosphorus produces severe diarrhea with loss of blood; damage to the liver, stomach, intestines, and circulatory system
(blood flow system); and coma. Swallowing a piece of white phosphorus no larger than 50 to 100 milligrams (0.0035 ounce) can even cause death.

Making lakes too healthy

T he second most important use of phosphate compounds is in making detergents. The compound most often used in detergents is called sodium tripolyphosphate, or STPP (Na5P3O10).

STPP adds a number of benefits to a detergent. For example, it can kill some bacteria and prevent washers from becoming corroded (rusted) and clogged. The most important function in detergents, however, is as a water-softening agent.

Natural water often contains chemicals that keep soaps and detergents from sudsing. They reduce the ability of soaps and detergents to clean clothes. STPP has the ability to capture these chemicals. It greatly improves the ability of soaps and detergents to make suds and clean clothes. The first detergent to use STPP was Tide, in 1947. The introduction of Tide brought about a revolution in clothes cleaning.

But STPP can create problems for the environment. After detergents have been used, they often end up in rivers and streams and, eventually, in lakes from waste water. And that's just fine for the algae that live in those lakes. Algae are tiny green plants that use phosphorus as they grow. As more detergents get into lakes, the amount of STPP increases. That means there is more phosphorus in a lake and that, in turn, means that algae begin to grow much faster.

In some cases, there is so much STPP and phosphorus in a lake that algae grow out of control, clogging the lake with algae and other green plants. The lake slowly turns into a swamp, and finally into a meadow. The lake disappears!

Many people became concerned about this problem in the 1960s. They demanded that less STPP be used in detergents. A number of cities and states banned the sale of STPP detergents. STPP production had grown rapidly from 1.10 billion pounds in 1955 to 2.44 billion pounds in 1970. But then production began to drop off. By the mid-1990s, production had dropped well below a billion pounds a year.

Interestingly, red phosphorus does not have the same effects. It is considered to be relatively safe. It is dangerous only if it contains white phosphorus mixed with it.

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Phosphorus

Phosphorus

Description

Phosphorus (chemical symbol P) is a mineral discovered by the German alchemist Henig Brand in 1699. It plays an essential part in multiple biochemical reactions for both plants and animals and is essential to all life. Phosphorus is found in living things, in soil and rock, mostly as chemical compounds known as phosphates. Rock and soil phosphorus are mined extensively throughout the world, but especially in the Peoples' Republic of China and the United States.

Phosphorus extracted from rock is classified as either white, red or black. White (also called yellow or common) phosphorus is a wax-like substance created by heating phosphate rock until it vaporizes and the condensation solidifies. One of this form's characteristics has given the English language the adjective phosphorescent, from white phosphorus's capacity to glow in the dark when exposed to air.

White phosphorus is highly toxic, causes burns if it comes in contact with skin, and is so combustible that it has to be stored underwater for safety. Red phosphorus is a rust-colored powder created by heating white phosphorus and exposing it to sunlight. It is not as combustible as the white form. Black phosphorus is made by heating white phosphorus under extremely high pressure until it resembles graphite.

In plants, phosphorus is necessary for photosynthesis to take place. In the human body, phosphorus works in tandem with another element, calcium , in much the same way that two other electrolyte components, sodium and potassium , do. Though phosphorus is found in every cell of the human body and accounts for 1% of the body's total weight, its primary function is working in conjunction with calcium to form teeth and bones.

Eighty-five percent of the phosphorus found in the body is located in these structures. In a delicately balanced chemical reaction, substances known as PTH (parathyroid hormone), Calcitonin, and 25-Dihydroxy vitamin D regulate the absorption of both calcium and phosphorus from the intestinal tract, thus making it available for the production of bones and teeth. If an excessive amount of phosphorus is absorbed, this will result in the phosphorus combining with all available calcium and preventing the calcium's efficient use in making and maintaining bones and teeth.

PTH balances the proportions of calcium and phosphorus in the body by increasing the release of calcium and phosphate from bone and the loss of phosphorus via the kidneys while limiting the excretion of calcium. PTH also increases the activity of the 25-Dihydroxy v25-Dihydroxy vitamin D , which, in contrast, increases the absorption of both phosphorus and calcium from the intestinal tract.

General use

White phosphorus is a component of fertilizers, detergents and water softeners. It is also used in the manufacture of steel, plastics, insecticides, medical drugs, and animal feeds. Both white and red phosphorus are used in the making of safety matches and pesticides, including rat poison.

But the 15% of this element found in the blood stream and in other soft tissue also has a highly significant part to play in a variety of other body functions. Working with Vitamin B, phosphorus is involved in the metabolism of fats and carbohydrates, in both the repair of damaged cells and tissues and the routine maintenance of healthy ones. Phosphorus is necessary for the regularity of the heartbeat, and aids in the contraction of all other muscles throughout the body. Phosphorus is needed for the functioning of the kidneys and plays a part in the conduction of impulses along the network that makes up the nervous system.

Preparations

According to the American Dietetic Association, phosphorus intake in the United States is generally above what is needed, and in recent years has actually increased. Therefore, under normal circumstances with normal food intake, there is seldom if ever a need to supplement intake of phosphorus. Persons suffering from eating disorders such as anorexia and bulimia can be deficient in phosphorus intake as well as other nutrients. As the best source of phosphorus is in protein foods such as meat, eggs and milk products, some vegetarians may also need to evaluate their intake of this element. Excess consumption of processed foods, and inadequate intake of whole foods, plus fertilizers and pesticides are some of the causes for excess phosphorus.

Beside high-protein foods, phosphorus is also found in decreasing quantities in whole grain breads and cereals, especially unprocessed ones, and in minute amounts in fruits and vegetables. The phosphorus present in whole grain breads and cereals, however, exists as a substance called phytin. Phytin combines with calcium to create a salt that the human body is incapable of absorbing, thus making unprocessed, unenriched grains a negligible source of phosphorus. But both commercially prepared cereals and breads may provide this element as they are frequently enriched with it. Phosphates can also be taken by mouth as a tablet.

Precautions

White phosphorus is poisonous. Red phosphorus is not. As noted, white phosphorus is a highly toxic, flammable substance capable of burning the skin if it makes contact, and of igniting at room temperature. It should be handled with extreme care. Accidental phosphorus poisoning can happen from both fertilizers and pesticides. Phosphates sometimes are leached into water systems through sewage and can drastically alter the chemical makeup of lakes and rivers. In sufficient quantities, they can lead to the death of nearly all forms of aquatic life.

A normal blood serum level of phosphorus is 2.4-4.1 mg per deciliter of blood. An abnormal serum phosphorus level should be evaluated by a physician.

Phosphorus levels higher than normal can indicate a diet that includes an excessive phosphorus intake, inadequate intake of calcium, or lack of PTH (parathyroid hormone) in the system. It can be related to bone metastasis associated with cancer , liver or kidney disease, or sarcoidosis.

Serum phosphorus levels that are below normal can be related to insufficient phosphorus or vitamin D in one's diet leading to rickets in children and osteomalacia in adults. Disorders of the parathyroid gland, causing it to secrete excessive quantities of PTH, or of the pancreas, causing it to secrete too much insulin, also affect blood levels of phosphorus. Diabetic ketoacidosis or too much calcium are other possible causes. Multiple endocrine neoplasia (MEN) is yet another condition that often is associated with lower than normal levels of phosphorus.

Side effects

Phosphorus preparations taken to supplement low phosphorus levels in the body can cause diarrhea .

Interactions

Antacids can decrease the absorption of phosphorus. Laxatives and enemas that contain the chemical compound sodium phosphate and excessive intake of vitamin D can increase phosphorus levels in the body. Administration of intravenous glucose solutions will cause phosphorus to combine with the glucose that is being absorbed by the cells.

BOOKS

PERIODICALS

Affenito, Sandra G., pH, RD, and Jane Kerstetter, pH, RD. "Position of the American Dietetic Association and Dietitians of Canada: Women's Health and Nutrition." Journal of the American Dietetic Association 1999.

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Phosphorus exhibits allotropy (i.e., it has multiple forms in the same physical state); the physical constants given above are for the common white phosphorus. White phosphorus is an extremely poisonous, yellow to white, waxy, solid substance, nearly insoluble in water but very soluble in carbon disulfide. When exposed to air it ignites spontaneously, burning to form white fumes of phosphorus pentoxide, P2O5. Because of its toxicity and pyrophoric nature, phosphorus is stored underwater. Contact with the skin may cause burns. White phosphorus is phosphorescent (i.e., glows without emitting heat).

When white phosphorus is heated to about 250°C in the absence of air, it changes into the more stable red phosphorus. This form appears as dull, reddish-brown cubic crystals or amorphous powder. Its specific gravity is 2.34. The red form is less dangerous than the white form, but should be handled with caution. It is insoluble in carbon disulfide and most other solvents. It does not ignite unless heated to about 200°C, does not phosphoresce, and is not poisonous. Another form of phosphorus is black phosphorus, a crystalline electrically conductive material similar to graphite in appearance. It was first prepared by P. W. Bridgman by heating white phosphorus to 200°C under a pressure of 12,000 atmospheres. Its specific gravity is 2.70.

Natural Occurrence and Commercial Preparation

Because of its chemical activity phosphorus does not occur uncombined in nature but is widely distributed in many minerals. A major source is apatite, an impure calcium phosphate mineral found in phosphate rocks. In the United States major deposits are found in Florida, Tennessee, Montana, and Idaho. White phosphorus is prepared commercially from phosphate rock in an electric furnace or blast furnace. The principal use of phosphorus is in compounds; for this reason, most of the phosphorus produced in furnaces is burned to make phosphorus pentoxide, a white powdery substance. While the pentoxide is used as a drying agent and chemical reagent, it is chiefly converted to phosphoric acid, H3PO4, also called orthophosphoric acid, by reaction with water. Another important source of phosphoric acid is from phosphate rocks by treatment with sulfuric acid; this is the so-called wet-acid process.

Biological Importance and Applications

Phosphorus is present in plants and animals. There is over 1 lb (454 grams) of phosphorus in the human body. It is a component of adenosine triphosphate (ATP), a fundamental energy source in living things. It is found in complex organic compounds in the blood, muscles, and nerves, and in calcium phosphate, the principal material in bones and teeth. Phosphorus compounds are essential in the diet. Organic phosphates, ferric phosphate, and tricalcium phosphate are added to foods. Dicalcium phosphate is added to animal feeds.

White phosphorus is used as a deoxidizing agent in the preparation of steel and phosphor bronze. It is also used in rat poisons and to make smoke screens (by burning) for warfare. Red phosphorus is used in making matches. The major use of phosphorus compounds is in fertilizers, especially in a mixture called superphosphate, obtained from phosphate minerals by sulfuric acid treatment; and in nitrophosphates. Phosphorus compounds are also used commercially in detergents, water softeners, pharmaceuticals, dentifrices, and in many other less important uses. Toxic nerve gases such as sarin contain phosphorus.

Phosphoric acid is primarily used in the production of phosphate compounds. It is also used in pickling metals, in sugar refining, and in soft drinks. Phosphorus forms a number of compounds with the halogens, e.g., the trichloride, PCl3, and the pentachloride, PCl5, both used as reagents. It also forms an oxychloride, POCl3. It reacts with sulfur to form a pentasulfide, P2S5, and a thiochloride, PSCl3, used in insecticides and oil additives. Phosphine, PH3, is a poisonous gas. Besides the pentoxide, phosphorus forms several other oxides; there are several acids other than the orthophosphoric acid noted above. Phosphorus also combines with various other nonmetals and with some metals.

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Phosphorus

Phosphorus

The element phosphorus is essential to living organisms. It is part of the backbone of DNA (deoxyribonucleic acid), the carrier and transmitter of genetic information in cells. The element and its compounds have many commercial applications.

Phosphorus was first isolated by the alchemist Hennig Brand of Hamburg around 1670. He prepared white phosphorus, one of two common forms (allotropes) of the element, by evaporating human urine and strongly heating the residual solids. White phosphorus distilled and was collected under water.

The two common forms of phosphorus are white, which is made up of P4 molecules, containing four atoms of phosphorus arranged in a regular tetrahedral formation, and red, which is a noncrystalline polymer. White phosphorus glows in the dark and bursts into flame in air. Red phosphorus does not react rapidly with air.

Phosphorus makes up about 0.12 percent of Earth's crust. It is extracted from minerals that contain phosphate (PO43−) groups. Large deposits of such minerals, of which the most important is fluorapatite, Ca5F(PO4)3, are found in the United States, Morocco, Russia, and Tunisia. At the present rate of extraction, the known deposits of phosphate rock would be sufficient to supply the world's demand for phosphorus for the next 1,000 years.

More than 90 percent of commercial phosphorus production is in the form of calcium salts of phosphoric acid, H3PO4, used as fertilizers. Other significant uses of phosphorus compounds are in the manufacture of matches (phosphorus sulfides), food products and beverages (purified phosphoric acid and its salts), detergents (sodium polyphosphates), plasticizers for polymers (esters of phosphoric acid), and pesticides (derivatives of phosphoric acid). Related to the phosphorus pesticides are nerve gases, poisonous compounds that rapidly attack the central nervous system, initially developed during World War II.

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phosphorus

phosphorus An essential element, occurring in tissues and foods as phosphate (salts of phosphoric acid), phospholipids, and phosphoproteins. In the body most (80%) is present in the skeleton and teeth as calcium phosphate (hydroxyapatite); the remainder is in the phospholipids of cell membranes, in nucleic acids, and in a variety of metabolic intermediates, including ATP. The parathyroid hormone controls the concentration of phosphate in the blood, mainly by modifying its excretion in the urine.

Adult needs (about 1.3 g per day) are always met. The calcium to phosphate ratio of infant foods is, however, important. Phosphate deficiency is common in livestock and gives rise to osteomalacia (also known as sweeny or creeping sickness).

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phosphorus

phosphorus (P) An element that is required by plants in the oxidized form, as orthophosphate (PO42+). The special chemical properties of orthophosphate are utilized in reactions in which energy is transferred, often involving ATP. It is also a good buffer, helping to maintain a neutral pH. The leaves of plants deficient in phosphate become dark green or blue-green and a reddish pigment may develop. Growth is generally reduced.

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phosphorus

phos·pho·rus
/ ˈfäsfərəs/
•
n.
the chemical element of atomic number 15, a poisonous, combustible nonmetal that exists in two common allotropic forms,
white phosphorus, a yellowish waxy solid that ignites spontaneously in air and glows in the dark, and
red phosphorus, a less reactive form used in making matches.
(Symbol: P)

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phosphorus

phosphorus Symbol P. A nonmetallic element that is a major essential element for living organisms. It is an important constituent of tissues (especially bones and teeth) and of cells, being required for the formation of nucleic acids and energy-carrying molecules (e.g. ATP) and also involved in various metabolic reactions.

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phosphorus

phosphorus(P) An element that is an essential nutrient for all living organisms. Plants require it in the oxidized form, as orthophosphate (PO2+4). The growth of phosphorus-deficient plants is usually reduced and their leaves become dark green or blue-green and a reddish pigment may develop.

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phosphorus

phosphorus (fos-fer-us) n. a nonmetallic element that is toxic in its pure state. Phosphorus compounds are major constituents in the tissues of both plants and animals. In humans, phosphorus is mostly concentrated in bone. Symbol: P.

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